Influence of target size and eccentricity on binocular summation of reaction time in kinetic perimetry

Interocular Transfer: The Dichoptic Flash-Lag Effect in Controls and Amblyopes

Purpose

The mammalian brain can take into account the neural delays in visual information transmission from the retina to the cortex when accurately localizing the instantaneous position of moving objects by motion extrapolation. In this study, we wanted to investigate whether such extrapolation mechanism operates in a comparable fashion between the eyes in normally sighted and amblyopic observers.

Methods

To measure interocular extrapolation, we adapted a dichoptic version of the flash-lag effect (FLE) paradigm, in which a flashed bar is perceived to lag behind a moving bar when their two positions are physically aligned. Twelve adult subjects with amblyopia and 12 healthy controls participated in the experiment. We measured the FLE magnitude of the subjects under binocular, monocular, and dichoptic conditions.

Results

In controls, the FLE magnitude of binocular condition was significantly smaller than that of monocular conditions (P ≤ 0.023), but there was no difference between monocular and dichoptic conditions. Subject with amblyopia exhibited a smaller FLE magnitude in the dichoptic condition when the moving bar was presented to the amblyopic eye and the flash to the fellow eye (DA condition) compared to the opposite way around (DF condition), consistent with a delay in the processing of the amblyopic eye (P = 0.041).

Conclusions

Our observations confirm that trajectory extrapolation mechanisms transfer between the eyes of normal observers. However, such transfer may be impaired in amblyopia. The smaller FLE magnitude in DA compared to DF in patients with amblyopia could be due to an interocular delay in the amblyopic visual system. The observation that normal controls present a smaller FLE in binocular conditions raises the question whether a larger FLE is or is not an indicator of better motion processing and extrapolation.

Binocular Vision and Stereopsis Across the Animal Kingdom

Most animals have at least some binocular overlap, i.e., a region of space that is viewed by both eyes. This reduces the overall visual field and raises the problem of combining two views of the world, seen from different vantage points, into a coherent whole. However, binocular vision also offers many potential advantages, including increased ability to see around obstacles and increased contrast sensitivity. One particularly interesting use for binocular vision is comparing information from both eyes to derive information about depth. There are many different ways in which this might be done, but in this review, I refer to them all under the general heading of stereopsis. This review examines the different possible uses of binocular vision and stereopsis and compares what is currently known about the neural basis of stereopsis in different taxa. Studying different animals helps us break free of preconceptions stemming from the way that stereopsis operates in human vision and provides new insights into the different possible forms of stereopsis. Expected final online publication date for the Annual Review of Vision Science, Volume 7 is September 2021. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

Comparison of monocular sensitivities measured with and without occlusion using the head-mounted perimeter imo

Purpose

Using a head-mounted perimeter imo that can measure monocular sensitivity with both eyes open, we investigated the difference between monocular sensitivities measured with and without occlusion of the fellow eye and if the difference was influenced by eccentricity.

Methods

Using the perimeter imo, monocular sensitivities with/without occlusion and binocular sensitivity were measured and compared. Three test conditions for monocular sensitivity without occlusion were: with/without a fusional fixation target, and a binocular random single eye test in which the target was randomly presented to either eye and the examinee was not aware of the tested eye. Within the central 25° visual field (VF), 29 points located at the fovea and on the 45°, 135°, 225°, and 315° meridians with 3° intervals were tested. Differences among the four monocular sensitivities with/without occlusion were further evaluated at the fovea, within and beyond the central 5° VF.

Results

Sixteen visually normal volunteers (mean age, 28.6 ± 4.6 years) were included in this study. Except at the fovea, monocular sensitivities measured without occlusion were significantly higher than those with occlusion (P < 0.01). No significant difference was seen among the three monocular sensitivities without occlusion (P = 0.82).

Conclusions

Except at the fovea, monocular sensitivities measured with and without occlusion significantly differed. This indicates that without occlusion, binocular interaction is activated and affects not only binocular sensitivity but also monocular sensitivity.

Effects of different levels of intraocular stray light on kinetic perimetry findings

PURPOSE

To evaluate the effect of different levels of intraocular stray light on kinetic perimetry findings.

METHODS

Twenty-five eyes of 25 healthy young participants were examined by automated kinetic perimetry (Octopus 900) using Goldmann stimuli III4e, I4e, I3e, I2e, and I1e. Each stimulus was presented with a velocity of 3°/s at 24 meridians with 15° intervals. Four levels of intraocular stray light were induced using non-white opacity filter (WOF) filters and WOFs applied to the clear plastic eye covers of the participants. The visual acuity, pupil diameter, isopter area, and kinetic sensitivity of each meridian were analyzed for each WOF density.

RESULTS

Visual acuity deteriorated with increasing WOF densities (p < 0.01). With a visual acuity of 0.1 LogMAR units, the isopter areas for III4e, I4e, I3e, I2e, and I1e decreased by -32.7 degree2 (-0.2%), -255.7 degree2 (-2.6%), -381.2 degree2 (-6.2%), -314.8 degree2 (-12.8%), and -59.2 degree2 (-15.2%), respectively; kinetic sensitivity for those stimuli decreased by -0.1 degree (-0.1%), -0.8 degree (-1.4%), -1.6 degree (-3.7%), -2.7 degree (-9.7%), and -1.7 degree (-16.2%), respectively. The pupil diameter with each WOF density was not significantly different.

CONCLUSION

Kinetic perimetry measurements with a high-intensity stimulus (i.e., III4e) were unaffected by intraocular stray light. In contrast, measurements with the I4e, I3e, I2e, and I1e stimuli, especially I2e and I1e, were affected. Changes in the shape of the isopter resulting from opacity must be monitored, especially in cases of smaller and lower-intensity stimuli.

Effect of Optical Defocus on the Kinetic Perimetry in Young Myopic Participants

PURPOSE

The prospective study evaluated the effects of optical defocus on kinetic sensitivity using automated kinetic perimetry.

MATERIALS AND METHODS

The 17 eyes of 17 healthy young participants were evaluated. All of the participants had myopia (≥ -5.00 D) and mild to no astigmatism (<1.00 D). Automated kinetic perimetry was performed using the Octopus 900 perimeter with Goldmann stimuli III4e, I4e, I3e, I2e, and I1e, with stimuli presented at 14 predetermined meridians, and a velocity of 3°/s. Optical defocus was induced with soft contact lenses, and varied in 1 D increments between 0 and +7 D. Kinetic sensitivity at each defocus was evaluated and compared to sensitivity with no defocus.

RESULTS

Although kinetic sensitivity with the III4e and I4e stimuli decreased slightly at the inferior nasal, total kinetic sensitivity measured with the III4e and I4e stimuli was unaffected by optical defocus. Conversely, kinetic sensitivity measured with the I3e, I2e, and I1e stimuli decreased at defocus greater than +6 D (p < 0.05), + 3 D (p < 0.01), and at a defocus greater than +1 D (p < 0.01), respectively.

CONCLUSIONS

Kinetic sensitivity was unaffected by defocus when measured with III4e and I4e stimuli. However, measurements with I3e, I2e, and I1e stimuli were affected, in particular measurements with I2e and I1e stimuli. Therefore, we conclude that optimal refractive correction with a contact lens or a spectacle lens is required in order to obtain accurate kinetic perimetry results, particularly for lower intensity stimuli.